The present invention relates to a multi-beam scanning device that projects an image on a screen.
Conventionally, a multi-beam light source as disclosed in Japanese Patent Provisional Publication No. 2000-249948 has been known. Such a multi-beam light source is used in a light scanning type image projector such as ones disclosed in Japanese Patent Provisional Publications No. 2002-296677 and No. 2002-300497. In the projector, light beams emerged from the multi-beam light source device are scanned on a screen to form an image thereon. Such an image projector can form a sharp image without an imaging optical system. It should be noted that the image optical system is required in a image projecting type projector in which light is passed through an LCD on which an image is formed, and the image is projected on the screen through the imaging optical system.
In the above-described image scanning type projector employing the multi-beam light source device, in order to scan the beams in a vertical direction, a galvano mirror is used. Generally, in the scanning type projecting device, the rocking movement is executed at a relatively high speed. Typically, several tens of reciprocating motions are executed accurately in one second. In order to achieve such high speed rocking movements accurately, rapid acceleration/deceleration should be done accurately. Therefore, the conventional scanning type projector employing the conventional multi-beam light source device is required to employ a high-accuracy controlling mechanism.
In the projector disclosed in Japanese Patent Provisional Publications No. 2002-296677, RGB (red, green and blue) beams are combined using a beam combining prism and the combined beam is scanned on the screen. However, such a beam combining prism is required to exhibit a reflection/transmission property that has wavelength selectivity. Such a prism is relatively expensive, which increases a manufacturing cost.
The projector disclosed in Japanese Patent Provisional Publication No. 2000-249948 is configured to scan a plurality of beams on the screen without using a converging lens. However, the projector as disclosed in this publication is configured such that split angles, which are angles formed between respective beams, are relatively large. Due to the large split angles, the beams are incident on an fθ lens at different incident angles in the scanning direction. Therefore, in such a case, uniformity of the scanning speed of the beams on the screen may be deteriorated, and a color shift may occur in the image formed on the screen.